Pharmacology of the Eye Flashcards
1
Q
Pupillary Response
A
Three muscles involved in pupil size (iris movement):
-
Dilator muscles in the iris (more outside portion of the iris)
- Fibers of this muscle are arranged radially
- Mostly α-adrenergic
- Contraction ⇒ pupil dilation
-
Pupillary sphincter muscles
- Circular band around the iris
- Have cholinergic receptors
- Contraction ⇒ pupil constriction
-
Ciliary muscles ⇒ located in the ciliary body
Two actions to provide for accommodation:- ⊕ with cholinergic agents ⇒ contraction ⇒ near vision
- ⊕ with adrenergic activity (mostly β) ⇒ relaxation ⇒ far vision
2
Q
Horner’s Syndrome
Clinical Manifestations
A
↓ SNS stimulation to the eye
- Unequal pupils (ipsilateral pupil dilated) ⇒ anisocoria
-
Ipsilateral lid ptosis
- SNS innervates the superior tarsal muscle (Muller’s muscle)
-
Ipsilateral eyebrow is raised
- Pt using voluntary facial muscles to keep the eye open
-
Irises are different colors (right is a few shades lighter than left)
- ↓ SNS stimulation to melanocytes
- Suggests condition has been there for at least a few years or is congenital
3
Q
Horner’s Syndrome
Pathophysiology
A
Hypothalamus (1st order neuron) ⇒ synapses around C8/T1 of spinal cord (2nd order neuron) ⇒ apex of the lung ⇒ under the subclavian artery ⇒ superior cervical ganglion (3rd order neuron) ⇒ eye ⇒ pupillary dilator muscle, Muller’s muscles, and ciliary muscle
- Congenital Horner’s is benign
- 50% of blockages in 1st or 2nd order sympathetics causing Horner’s are associated with tumors
- Tumor in the apex of the lung ⇒ Pancoast tumor
- Horner’s arising from a 3rd order deficit is usually not associated with tumor
4
Q
Horner’s Syndrome
Clinical Evaluation
A
To test for Horner’s:
-
Cocaine
- ⊗ NE re-uptake ⇒ ↑ existing stimulation
- Administer a drop of 10% solution of cocaine in each eye
- Normal eye ⇒ pupil dilation as expected
-
Affected eye ⇒ no effect
- No NE being released, so cocaine blocks reuptake of nothing
-
Apraclonidine may also be used
- α2 adrenergic agonist with weak α1 activity
- Receptors in effected eye are supersensitive
- Affected eye ⇒ pupil dilation
- Normal eye ⇒ no effect
-
Hydroxyamphetamine (Paredrine)
- Indirect α-adrenergic agonist ⇒ ↑ release of NE ⇒ dilation
- Differentiate 1st and 2nd order from 3rd order Horner’s
- Only 3rd order neurons are stimulated by eye drops
- Will cause pupil dilation in normal and affected eye except with 3rd order defects
5
Q
Horner’s Syndrome vs Physiologic Anisocoria
A
Horner’s Syndrome vs Physiologic anisocoria (20% of all people)
- Look at lid position ⇒ down in eye with smaller pupil ⇒ Horner’s syndrome possible
-
Stimulate SNS via light reflex ⇒ pupil dilation
- Physiologic anisocoria ⇒ both pupils dilate ⇒ pupils “equally unequal”
- Difference in size will remain constant
- Horner’s ⇒ only normal pupil dilates ⇒ difference in size will increase in dim ligh
- Then do cocaine/hydroxyamphetamine (Paredrine) tests
- Physiologic anisocoria ⇒ both pupils dilate ⇒ pupils “equally unequal”
6
Q
Mydriasis
Etiologies
A
↓ PNS stimulation ⇒ ↑ pupil size
-
Adie’s (tonic) pupil
- 70% of cases in young women from teens to 30’s
- 50-90% of these pts will have ↓ DTRs
- Pupil very slow to constrict and very slow to dilate in response to light
- Usually caused by damage to the post-ganglionic parasympathetic fibers (from the ciliary ganglion to the iris)
- May be seen in headaches, viruses, etc.
- Is benign but need to be able to diagnose it
- 70% of cases in young women from teens to 30’s
-
Iris damage (due to trauma)
- Smaller or larger pupil can be abnormal
-
Pharmacologic dilation of one eye
- Deliberate or inadvertent inoculation with pharmacological dilators
- Exposure to Jimson weed (contains bella donna alkaloids, an atropine-like substance)
- Transdermal patches used for travel sickness prevention (scopolamine)
-
Third nerve palsy
- Efferent fibers from the Edinger-Westphal nucleus come through CN-III to the pupillary sphincter
7
Q
Mydriasis
Clinical Evaluation
A
Pilocarpine ⇒ ⊕ PNS ⇒ pupil constriction
-
⅛% Pilocarpine solution
- Too weak to constrict a normal pupil
- Adie’s pupil ⇒ denervation hypersensitivity ⇒ pupil constriction by 1/8 ⅛% Pilocarpine
- Takes some time to develop
-
1% Pilocarpine solution
- Contricts all pupils that are not pharmacologically dilated
- B/l constriction r/o pharmacological dilation ⇒ suspect CN III palsy
8
Q
Anisocoria
Diagnosis
A
9
Q
Cycloplegic Agent
A
Relaxes accommodation / Relaxes pupillary constriction
10
Q
Mydriatic Agent
A
Dilates pupil
11
Q
Dilating Drops
A
-
Cholinergic antagonists ⇒ ⊗ effects of ACh @ muscarinic receptors on the iris and ciliary body
- Do not actively dilate the pupil
- Relax constriction and accommodation
-
Drugs include:
- Atropine
- Tropicamide
- Cyclopentolate
- Homatropine
- Scopolamine
-
Sympathetic agonists ⇒ ⊕ effects of NE @ adreneric receptors on the iris and ciliary body
- Activates dilation
-
Drugs include:
- Phenylephrine
REMEMBER TO DO THE FLASHLIGHT TEST TO CHECK FOR NARROW ANTERIOR CHAMBER ANGLES BEFORE YOU DILATE PATIENTS ‘ EYES.
12
Q
Atropine
A
- Naturally occurring alkaloid first isolated from the belladonna plant
- The most potent dilating drug
- Effects can last two weeks
-
Used when long-term dilation is necessary
- Very bad iritis or uveitis
- Following eye surgery
13
Q
Tropicamide
(Mydriacyl)
A
- Fastest acting ⇒ max effect in ~ 30 mins
- Shortest duration of action ⇒ lasts 4-6 hours
- 0.5% used for fundus exams
- Adequate to use when determining refraction errors in children
14
Q
Cyclopentolate
(Cyclogyl)
A
- Slightly stronger than Tropicamide
- Lasts up to 24 hours
- Given several times per day for prolonged effect
-
Indications:
- Used in children to determine accurate refraction correction
-
Corneal abrasions
- Pain ass. w/ corneal abrasion d/t ciliary muscle spasm,
- Pupil dilation and relaxing accommodation will make the pt more comfortable
- Mild conditions where you want the eye relaxed for a few days
15
Q
Homatropine
A
- Effects last 1-3 days
-
Prescribed 4x/day for:
- Corneal abrasions
- Chemical burns to the eyes
- Iritis or uveitis
- Post-operatively
